1. Field of the Invention
The present invention relates to a decorative member covered with a hard carbon layer.
2. Prior Art
Conventionally, decorative members, containing watch components such as watch cases and watch bands; ornaments such as cuff buttons, metal parts for bags, lighters; finger rings, necklaces, piercing earrings and brooches; frames for eyeglasses; and line guides such as fishing line guides and fiber guides, have required not only ornament or decorative value but high resistance to abrasion or wear. There are a decorative member formed from a metal having a tonality similar to the real color of gold, which has a gold-plated surface on a base metal made of brass or the like (see Japanese Patent Publication JP-A 8-120481). Decorative members are also known to be made of ceramics as a base, whose surface were covered with titanium nitride and shows a golden color, more excellent in wear resistance than gold is (see Japanese Patent Publication JP-A 1-265841).
However, the decorative members mentioned above which are made of the metal have problems in regard to weatherability, corrosion and abrasion resistance and their very short lifetime in use. In addition, in the case where Ni is included in the metal of a decorative member, there is a risk that some people is affected by metal allergy if the decorative member is put on.
Although a gold-plated decorative member has golden brilliancy in its early stage of use, it is poor in corrosion in an environment in which acid or alkaline chemicals are used, and subjected to a surface injury since gold is a soft metal, so that there has arisen another problem that its peculiar brilliancy is lost over its repeated uses.
While a decorative member covered with titanium nitride is excellent in abrasion resistance as compared with the decorative members as shown above, a longer stability of the resistance has additionally been demanded.
There has been proposed, for the purpose of a superficial protection of the surface, formation of a layer made of hard carbon such as diamond on a surface of gold and its alloy in Japanese Patent publications JP-A 62-180071 and JP-A 1-244705).
However, hard carbon layers, described in the Japanese Patent publications JP-A 62-180071 and JP-A 1-244705 above, made of a high purity diamond formed by means of Plasma CVD process or the like. Such high purity diamond layers are conspicuous in diamond crystal growth, therefore there was the problem that the crystal grains are too large to form a thin layer and the formation of a sounder layer formation requires some degree of thickness.
Furthermore, there are minute asperities on the surface made of the diamond layer of the member to cause irregular reflection of light on the surface. The problem of irregularly reflecting light on the surface can be solved by polishing the layer surface, but it takes a very long time for the mirror-polishing of the hardened surface of the diamond layer, whereby productivity is much decreased. Still besides, there was a problem that crystal grain boundaries are in this diamond layer and a number of voids are present in the bulk of the layer, causing local corrosion to occur by the chemicals easily.